godot-docs/tutorials/3d/csg_tools.rst

.. _doc_csg_tools:

CSG
===

CSG stands for **Constructive Solid Geometry**, and is a tool to combine basic
shapes or custom meshes to create more complex shapes. In 3D modelling software,
CSG is mostly known as "Boolean Operators".

Level prototyping is one of the main uses of CSG in Godot. This technique allows
users to create simple versions of most common shapes by combining primitives.
Interior environments can be created by using inverted primitives.

.. image:: img/csg.gif

Introduction to CSG nodes
-------------------------

Like other features of Godot, CSG is supported in the form of nodes. These are
the CSG nodes:

- :ref:`CSGBox <class_CSGBox>`
- :ref:`CSGCylinder <class_CSGCylinder>` (also supports cone)
- :ref:`CSGSphere <class_CSGSphere>`
- :ref:`CSGTorus <class_CSGTorus>`
- :ref:`CSGPolygon <class_CSGPolygon>`
- :ref:`CSGMesh <class_CSGMesh>`
- :ref:`CSGCombiner <class_CSGcombiner>`

.. image:: img/csg_nodes.png

.. image:: img/csg_mesh.png

CSG tools features
~~~~~~~~~~~~~~~~~~

Every CSG node supports 3 kinds of boolean operations:

- **Union:** Geometry of both primitives is merged, intersecting geometry
  is removed.
- **Intersection:** Only intersecting geometry remains, the rest is removed.
- **Subtraction:** The second shape is subtracted from the first, leaving a dent
  with its shape.

.. image:: img/csg_operation_menu.png

.. image:: img/csg_operation.png

CSGPolygon
~~~~~~~~~~

The :ref:`CSGPolygon <class_CSGPolygon>` node extrude along a Polygon drawn in
2D (in X,Y coordinates) in the following ways:

- **Depth:** Extruded back a given amount.
- **Spin:** Extruded while spinning around its origin.
- **Path:** Extruded along a Path node. This operation is commonly called
  lofting.

.. image:: img/csg_poly_mode.png

.. image:: img/csg_poly.png

.. note:: The **Path** mode must be provided with a :ref:`Path <class_Path>`
          node to work. In the Path node, draw the path and the polygon in
          CSGPolygon will extrude along the given path.


Custom meshes
~~~~~~~~~~~~~

Any mesh can be used for :ref:`CSGMesh <class_CSGMesh>`; the mesh can be
modelled in other software and imported into Godot. Multiple materials are
supported. There are some restrictions for geometry:

- it must be closed,
- it must not self-intersect,
- it must not contain internal faces,
- every edge must connect to only two other faces.

.. image:: img/csg_custom_mesh.png

CSGCombiner
~~~~~~~~~~~

The :ref:`CSGCombiner <class_CSGCombiner>` node is an empty shape used for
organization. It will only combine children nodes.

Processing order
~~~~~~~~~~~~~~~~

Every CSG node will first process its children nodes and their operations:
union, intersection or subtraction, in tree order, and apply them to itself one
after the other.

.. note:: In the interest of performance, make sure CSG geometry remains
          relatively simple, as complex meshes can take a while to process.
          If adding objects together (such as table and room objects), create
          them as separate CSG trees. Forcing too many objects in a single tree
          will eventually start affecting performance.
          Only use binary operations where you actually need them.

Prototyping a level
-------------------

We will prototype a room to practice the use of CSG tools.

.. tip:: Working in **Orthogonal** projection gives a better view when combining
         the CSG shapes.

Our level will contain these objects:

- a room,
- a bed,
- a lamp,
- a desk,
- a bookshelf.

Create a scene with a Spatial node as root node.

.. tip:: The default lighting of the environment doesn't provide clear shading
         at some angles. Change the display mode using **Display Overdraw** in
         the 3D viewport menu, or add a DirectionalLight node to help you see
         clearly.

.. image:: img/csg_overdraw.png

Create a CSGBox and name it ``room``, enable **Invert Faces** and change the
dimensions of your room.

.. image:: img/csg_room.png

.. image:: img/csg_room_invert.png

Next, create a CSGCombiner and name it ``desk``.

A desk has one surface and 4 legs:

- Create 1 CSGBox children node in **Union** mode for the surface
  and adjust the dimensions.
- Create 4 CSGBox children nodes in **Union** mode for the legs
  and adjust the dimensions.

Adjust their placement to resemble a desk.

.. image:: img/csg_desk.png

.. note:: CSG nodes inside a CSGCombiner will only process their operation
          within the combiner. Therefore, CSGCombiners are used to organize
          CSG nodes.

Create a CSGCombiner and name it ``bed``.

Our bed consists of 3 parts: the bed, the mattress and a pillow. Create a CSGBox
and adjust its dimension for the bed. Create another CSGBox and adjust its
dimension for the mattress.

.. image:: img/csg_bed_mat.png

We will create another CSGCombiner named ``pillow`` as the child of  ``bed``.
The scene tree should look like this:

.. image:: img/csg_bed_tree.png

We will combine 3 CSGSphere nodes in **Union** mode to form a pillow. Scale the
Y axis of the spheres and enable **Smooth Faces**.

.. image:: img/csg_pillow_smooth.png

Select the ``pillow`` node and switch the mode to **Subtraction**; the combined
spheres will cut a hole into the mattress.

.. image:: img/csg_pillow_hole.png

Try to re-parent the ``pillow`` node to the root ``Spatial`` node; the hole will
disappear.

.. note:: This is to illustrate the effect of CSG processing order.
          Since the root node is not a CSG node, the CSGCombiner nodes are
          the end of the operations; this shows the use of CSGCombiner to
          organize the CSG scene.

Undo the re-parent after observing the effect. The bed you've built should look
like this:

.. image:: img/csg_bed.png

Create a CSGCombiner and name it ``lamp``.

A lamp consists of 3 parts: the stand, the pole and the lampshade.
Create a CSGCylinder, enable the **Cone** option and make it the stand. Create
another CSGCylinder and adjust the dimensions to use it as a pole.

.. image:: img/csg_lamp_pole_stand.png

We will use a CSGPolygon for the lampshade. Use the **Spin** mode for the
CSGPolygon and draw a `trapezoid <https://en.wikipedia.org/wiki/Trapezoid>`_
while in **Front View** (numeric keypad 1); this shape will extrude around the
origin and form the lampshade.

.. image:: img/csg_lamp_spin.png

.. image:: img/csg_lamp_polygon.png

.. image:: img/csg_lamp_extrude.png

Adjust the placement of the 3 parts to make it look like a lamp.

.. image:: img/csg_lamp.png

Create a CSGCombiner and name it ``bookshelf``.

We will use 3 CSGBox nodes for the bookshelf. Create a CSGBox and adjust its
dimensions; this will be the size of the bookshelf.

.. image:: img/csg_shelf_big.png

Duplicate the CSGBox and shorten the dimensions of each axis and change the mode
to **Subtraction**.

.. image:: img/csg_shelf_subtract.png

.. image:: img/csg_shelf_subtract_menu.png

You've almost built a shelf. Create one more CSGBox for dividing the shelf into
two levels.

.. image:: img/csg_shelf.png

Position your furniture in your room as you like and your scene should look
this:

.. image:: img/csg_room_result.png

You've successfully prototyped a room level with the CSG tools in Godot.
CSG tools can be used for designing all kinds of levels, such as a maze
or a city; explore its limitations when designing your game.